This invention relates to cathode ray display tubes and to channel plate electron multipliers for use therein.
The invention is concerned particularly with a cathode ray display tube comprising means for producing an electron beam, a channel plate electron multiplier for producing at its output side current multiplied electron beams in response to the electron multiplier being scanned by the electron beam over its input side, the channel plate electron multiplier comprising a stack of a plurality of apertured dynodes, the apertures of the dynodes being aligned to provide channels through the stack, a phosphor screen comprising repeating groups of phosphor elements and colour selection means operable to direct selectively the elcctron beams from the channel multiplier onto the respective phosphor elements.
A cathode ray display tube of the aforementioned kind is described in British Patent Specification No. 2,124,017A corresponding to U.S. Pat. No. 4,560,898. In this tube, the phosphor screen comprises a repeating pattern of horizontally separated R (red), G (green) and B (blue) phosphor elements, typically in the form of vertical lines of phosphor material, with each group of three-colour phosphor elements, i.e. triplet, associated with a respective channel of the muliiplier. The dynode apertures are all circularly symmetrical with circular cross-section entrances and exits. A current multiplied electron beam emerging from the output side of the multiplier, and extracted with the aid of an apertured extractor electrode, is directionally controlled by the colour selection means so as to impinge upon one of the three phosphor elements as appropriate. The colour selection means is in the form of a deflection electrode arrangement having a pair of electrodes located on either side of the axis of each channel of the multiplier which are selectively energisible to deflect the output electron beam for example to one side or the other in order to impinge upon the two outer phosphor elements respectively of the associated group or to allow the electron beam to pass generally straight through, with a small amount of deflection if necessary, to impinge on the central phosphor element.
Such a colour display tube enables a reasonable resolution to be achieved but an improvement in its perfrrmance in this respect would be advantageous, particularly for certain tube applications.